PSI - Issue 19

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Michele Zanetti et al. / Procedia Structural Integrity 19 (2019) 627–636 M. Zanetti / Structural Integrity Procedia 00 (2019) 000–000

Table 4: Example of the method used to calculate FAT classes adopting the PSM.

It is noted that in results as not been reported load conditions ‘out of plane bending’ for track pipe, referred to Table 3, because they are not considered the most critical loading conditions. Some remarks that emerges from results reported in Table 5 can be stated as follows.  FAT classes taken from Design Standards are higher than those obtained from the PSM approach. This is due to the difficulty to find the appropriate geometry in the Design Standards, which is consistent with the analysed detail, in particular when geometries are complex.  The PSM allows to evaluate comparatively the fatigue criticality at the toe and at the root (fillet or partial penetration weld).  From results obtained adopting PSM emerges that, for several loading conditions (in particular for load-carrying fillet welds: axC/axT, ipbC/ipbT, opbC/opbT ), a fillet weld leads to a reduction of the fatigue strength class as compared to a full penetration weld (from 15% to 25%). It is also observed that the weld root is never the most critical point. Direct application of PSM After reporting on the use of the PSM to estimate FAT classes in terms of nominal stress, a case study describing the direct application of the PSM is reported in this section, to tackle the fatigue strength assessment of two geometrically complex welded joints of a lattice-type connection (node A and node B of Figure 2). Figure 2 reports the loading condition studied, which consist of 4 vertical forces (40 kN each) applied to track pipes. 